Separating reserved identifiers in flex

I have a language I am making a parser for which contains function calls. A few function names are reserved and I would like to handle them differently in my grammer. In EBNF it would look like

FunctionCall ::= FunctionName '(' ')'
SpecialFunctionCall :: SpecialName '(' ')'

FunctionName ::= VariableName - SpecialFunctionName

SpecialFunctionName ::= "special_function_a" | "special_function_b"

My problem is in translating the exception operator from EBNF to flex.

FunctionName    {Letter}{LetterOrDigit}

Is a super set of SpecialFunctionName, which is a 开发者_如何学Pythonhard-coded string

SpecialFunctionName   "special_function_a" | "special_function_b"

Hence I get a warning from bison saying that SpecialFunction will never be matched. Should I merge the tokens and compare the strings in the parser, or is there a recommended way to resolve this ambiguity in in flex?

The normal way of dealing with this to have the lexical analyzer recognize the special names and return the correct token type (SpecialName) for the special names and a regular identifier token (apparently FunctionName) for the other tokens.

However, it normally requires an undue degree of prescience on the part of the lexical analyzer to say that a particular (non-reserved, non-special) word is a function name rather than a simple identifier (which could also be a simple variable - unless you've gone down the Perl route of using sigils to identify variables from functions).

As long as you put the SpecialFunction rule FIRST in the lexer file:

{SpecialFunctionName}    { return SpecialName; }
{FunctionName}           { return FunctionName; }

any identifer that matches both patterns will trigger the first rule and thus return SpecialName instead of FunctionName.